The invention concerns an indicator chamber (optode) comprising an indicator and a membrane surrounding the indicator and impermeable to it for measurement of concentrations of substance particles by means of e.g. a light measurement system, such as a light source, light receiver and readout means. In particular, the invention concerns the material used for filling the optode.
The known systems operate on the principle that the portion of a composition to be measured in separated from components which disturb the accuracy of measurement. If, for example, the oxygen content of blood is to be determined through fluorescence methods, certain protein fractions would render the direct readings inaccurate due either to their own fluorescence or through binding of the indicator. Through separation of the measurement area by means of a membrane, through which the fraction to be measured diffuses, the blood protein fractions and other components are held back, thereby preventing their affecting the accuracy of measurement.
A disadvantage of these systems lies in the fact that the indicators used are not terribly selective, and thus would react with other components than that to be measured, or in that no species-specific indicators are available. In this, the applicability of the method is restricted. This is in particular unfortunate, in that the method employed requires a lower level of the component to be measured than other methods, and in addition is robust and directly applicable without preparation. With respect to the nature and operation of the optodes, the entire teachings of U.S. Pat. No. 4,003,707 are hereby incorporated by reference.